The present invention relates to a bonding composition and more particulary to a method of attaching an ultrasonic transducer to a surface with the bonding composition. It is frequently necessary to bond ultrasonic transducers to surfaces in an environment in which the bonding material will be subject to high temperatures and radiation. One example is the ultrasonic transducers which are used to monitor the vibration of a core barrel in a nuclear reactor. The bonding material in these situations may be subjected to temperatures as high as 600.degree. F and radiation levels as high as 50R (Roentgen) per hour. Investigations have shown that conventional, commercially available ultrasonic couplants are unsuitable for such conditions. For example, the commonly available colloidal grease type couplants will exhibit an excessive degree of thermal outgassing with eventual loss of physical properties and loss of mechanical bonding. Such changes would initially lead to constantly changing ultrasonic modulation which could generate erroneous ultrasonic data. Based on outgassing data, the in-service lift of common high temperature couplants would be no greater than 700 hours at the temperatures encountered in nuclear reactor service. It is further estimated that under irradiation conditions, and with subsequent loss of adhesion and mechanical properties due to both the thermal and irradiation embrittlement the useful service life of commercial couplants would be no greater than 50 hours. Because of this relatively short predicted service life, frequent changing of the couplant would be necessary. Radiation exposure levels as well as inaccessiblity of the monitoring sites would make such a practice prohibitive.
Alternatives to the collodial grease type couplants which have been considered are alloys solder bonding systems, thermosetting resin systems and ceramic adhesives all with little or no success in such an environment. One method of coupling which has been developed for use at the high temperature and radiation level referred to above employs a room temperature vulcanizing material formed from either vinyl methyl siloxane or polyphenyl siloxane. The special compounding of these materials makes them temperature and radiation stable and conductive so that the couplant also serves as one of the electrical connections to the transducer. This method of coupling is disclosed and claimed in the co-pending patent application of the present inventor, Ser. No. 517,972 filed Oct.25, 1974, now U.S. Pat. No. 3,970,504.